Data Extraction for the Oracle Warehouse
Oracle Tips by Burleson Consulting
High Performance Data Warehousing
Data Extraction For The Oracle Warehouse
As we know, most data warehouses are
loaded in batch mode after the online system has been shut down. In
this sense, a data warehouse is bimodal, with a highly intensive
loading window, and an intensive read-only window during the day.
Because many data warehouses collect data from non-relational
databases such as IMS or CA-IDMS, no standard methods for extracting
data are available for loading into a warehouse. However, there are
a few common techniques for extracting and loading data, including:
* Log “sniffing”--Applying archived redo logs from the OLTP system
to a data warehouse.
* Using update, insert, and delete triggers--Firing-off a
distributed update to a data warehouse.
* Using snapshot logs to populate the data warehouse--Using log
files to update replicated table changes.
* Running nightly extract/load programs--Using extracts to retrieve
operational data and load it into a warehouse.
For details about data extraction and loading of Oracle warehouses,
see Chapter 11, Oracle Data Warehouse Utilities.
Several methods can be used to aggregate data within OLAP servers.
As you can see in Figure 1.16, this method extracts data from the
relational engine and summarizes the data for display. Another
popular method pre-aggregates the data and keeps the summarized data
ready for retrieval.
Figure 1.16 Aggregation and OLAP servers.
For details about data aggregation in Oracle warehouses, see Chapter
10, Aggregating Data For Oracle Warehouses.
This is an excerpt from "High Performance
Data Warehousing", copyright 1997.
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